Mortgage Overpayment Calculator
See how much interest and time you save by overpaying your mortgage each month or paying a lump sum. Side-by-side balance table included.
Reviewed by Dany, RightSums team · Updated
Runs in your browser. Free, no sign-up.
personal-finance · Daily life · UK
Enter your mortgage balance, interest rate and the time left, then add a regular monthly overpayment, a one-off lump sum, or both. You can choose the month the lump sum goes in. The calculator keeps your normal payment the same and lets the overpayments shorten the term. It shows the interest you save, how much sooner you finish and your new term, with a year-by-year table comparing your balance with and without overpaying. It flags when you would overpay more than 10% of your balance in the first year, a common lender allowance. The rate is treated as fixed and interest is worked out monthly. Early repayment charges are not included, so check your lender's terms first.
Accepted inputs
- Mortgage balance
- Interest rate (% a year)
- Years and months left
- Monthly overpayment
- One-off lump sum
- Month the lump sum is paid
Outputs
- Interest saved
- Time saved
- New mortgage term
- Normal monthly payment
- Year-by-year balance with and without overpayments
How to use the Mortgage Overpayment Calculator
- Enter what you owe today, your interest rate and the years and months left on your mortgage.
- Add an extra amount to pay each month, a one-off lump sum, or both.
- If you add a lump sum, enter the month you plan to pay it, where 1 means now.
- Read the interest saved, the time saved and the side-by-side balance for each year.
Frequently asked questions
How much will I save if I overpay my mortgage by £100 a month?
On a £200,000 mortgage at 4.5% with 25 years left, paying £100 a month on top of the normal £1,111.66 saves about £21,142 in interest. You would finish 3 years and 6 months early. Doubling it to £200 a month saves about £36,280 and 6 years 1 month.
How much can I overpay my mortgage without a penalty?
It depends on your lender. MoneyHelper says many lenders will let you overpay up to 10% a year without penalties. On a £200,000 balance, 10% is £20,000. Paying more than your deal allows can trigger an early repayment charge, so check your mortgage terms before you pay.
Is it better to overpay monthly or pay a lump sum?
Money paid earlier saves more, because it stops interest sooner. On £200,000 at 4.5% over 25 years, a £10,000 lump sum paid now saves about £19,300. Paid a year later it saves about £18,072. A regular £100 a month adds up to more over time and saves about £21,142.
Does overpaying reduce my term or my monthly payment?
This calculator keeps your monthly payment the same, so overpaying shortens the term. Some lenders instead recalculate and lower your monthly payment while keeping the end date. Ask your lender which they do, as keeping the payment the same usually saves more interest.
Should I overpay my mortgage or save the money?
Overpaying saves interest at your mortgage rate, so it tends to pay off when your mortgage rate is higher than the after-tax rate on your savings. MoneyHelper suggests clearing dearer debts first and keeping at least three months of money in reserve. This tool shows the saving, not which choice suits you.
Sources
The rates and rules in this tool come from:
Guides that use this tool
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